1. Field of the Invention
The present invention relates generally to electronic device testing, and more particularly, to synchronization techniques used in testing integrated circuit (IC) devices with a test apparatus that has multiple instruments.
2. Description of the Related Art
A test system having a multiple instrument platform represents a significant advance in the art. One example of such a test system is described in U.S. patent application Ser. No. 10/222,191, entitled “Circuit Testing with Ring-Connected Test Instrument Modules,” filed Aug. 16, 2002, the entire contents of which are incorporated by reference herein.
In this test system 100, illustrated in FIG. 1, a test head interface module 110 and a plurality of instruments (collectively referred to as 120; individually referred to as instrument A, instrument B, and instrument C) are connected together over a ring bus 130. The test head interface module 110 houses a global clock 140 to which all of the instruments 120 are synchronized.
During testing, the test system 100 operates under the control of software, e.g., a test program. The test program specifies the test patterns to be supplied to a device under test (DUT) 150, the expect data patterns to be compared with the response signals from the DUT 150, and timing information indicating when the test patterns are to be supplied and when the response signals are to be strobed.
With a multiple instrument platform, the designer of a test has the flexibility to simultaneously test different pins of the DUT 150 with different test patterns and to condition the triggering of this test with respect to certain programmed events or certain events detected at the DUT 150. In addition, the test system having a multiple instrument platform is able to accommodate testing of pins at different clock rates. For example, if the core part of the DUT 150 operates at 250 MHz and other parts of the DUT 150 operates at 100 MHz, the pins corresponding to the core part are tested with instruments running at 250 MHz and the pins corresponding to the other parts are tested with instruments running at 100 MHz.
In order for the triggering across different instruments to be carried out accurately, the instruments must be synchronized with respect to each other so that the test data generated by the instruments arrive at the pins of the DUT 150 at the time specified in the test program. The synchronization of the instruments with respect to the global clock ensures that trigger processing begins at the same time at each instrument, but this is not sufficient for synchronizing the instruments with respect to each other because: (i) the delays associated with the hardware overhead during trigger generation and reception differ from instrument to instrument; (ii) the instruments exhibit different pipeline delays; and (iii) the instruments may operate at different clock rates.